1. Field of the Invention
The present invention relates to a process of producing a high alloy layer on a surface of a casted workpiece. More particularly, the present invention pertains to a process of producing a high alloy layer on a specific part of a surface of a casted workpiece.
2. Description of Prior Art
Various proposals have hithertofore been made for producing a high alloy layer on a specific part of a surface of a casted workpiece in order for improving various properties such as wear-resistant property, corrosion-resistant property and heat-resistant property of the surface part. Among such proposals, processes applicable to iron-based castings are classified into two groups, one being the process wherein the specific part is alloyed after the casting is moulded and the other being the process wherein the specific part is alloyed while the workpiece is being moulded. The former process is considered as being disadvantageous from the economical point of view in that additional steps and facilities are required for alloying. In the latter process, alloying metals or mixtures of the alloying metal powders and suitable binders such as synthetic resins are attached in advance to surfaces of casting moulds corresponding to the specific parts of the workpieces where the alloyings are to be made and casting steps are carried out by pouring molten cast metal into the moulds to thereby form alloys on the specific parts of the casted workpieces under the heat of the molten metal. For example, Japanese patent publication No. 52-730 proposes to provide a mixture of powders of metal carbides and a liquid binder such as triethyleneglycol and apply the mixture to a desired part of the mould surface to form a film by having the mixture dried. A following casting steps will then produce an alloy on a desired part of the casted workpiece due to the existence of the metal carbides. The proposed process is however disadvantageous in that the binder is resolved under the heat of the molten casting metal producing gaseous products which cause pin holes and voids in the casted workpiece.
Japanese patent publication No. 52-731 proposes to provide a mixture of powders of a metal or an alloy and powders of thermosetting resin and form the mixture under heat into a piece of a desired shape. The piece is then applied to a desired part of the casting mould before the molten casting metal is poured into the mould. This process is also disadvantageous in that the thermosetting resin is resolved under the heat of the molten metal producing gaseous products. Japanese patent publication No. 53-18166 proposes to provide a mixture of powders of an alloy containing Te, Cu and S and powders of graphite. The mixture is then added with alcohol and applied to a desired part of the casting mould. Thereafter, molten metal containing C, Si, Mn, V, Ni and Fe is poured into the mould. The proposed process is disadvantageous in that it can be applied only to casting metal of a specific composition.